<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" href="c1.css">

</head>
<body>
    <div style="color: blue">
        div1div1div1
    </div>
    <div class = "c1">
        div2div2div2
    </div>
    <div class = "c3">
        div3div3div3
    </div>
    <div class = "c2 c1">
        div4div4div4
    </div>
    <a id="uu" class="c1" href="https://baidu.com" style="color: green">百度</a>

</body>
</html>